In recent years, living radical polymerization methods are known as one of the techniques for polymerizing vinyl monomers. In a living radical polymerization method, it is generally relatively easy to control the molecular weight of the obtained vinyl polymers.
It is also possible to achieve a narrower molecular weight distribution of vinyl polymers contained in the obtained polymers, and it is thus possible to easily produce polymers having a ratio (Mw/Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn), which is used as an index thereof, of 2 or less. The molecular weight and molecular weight distribution affect the physical characteristics of the obtained polymers, and living radical polymerization methods are thus expected to be used to control the physical characteristics of polymers.
In a living radical polymerization method, a living radical polymerization reaction using a transition metal complex catalyst has previously been known. As for transition metal complex catalysts, a complex must be obtained by using a metal, such as Cu, Ni, Re, Rh, or Ru, as a central metal, and designing a ligand. The use of a transition metal complex catalyst requires a large amount of the catalyst, and it is difficult to remove the catalyst after the polymerization reaction.
Many of these metals are highly toxic, possibly causing problems in terms of, for example, environment and toxicity in the organism. Additionally, ligands are in many cases expensive, or require complicated steps for synthesis.
To solve these problems, the present inventor et at has developed a nonmetallic element compound, such as an imidazolium iodide, as a living radical polymerization catalyst (Patent Literature (PTL) 1). The catalyst of PTL 1, which is free from a transition metal, is excellent in terms of safety as well as cost, since the use of expensive ligands is unnecessary.
However, the development of a living radical polymerization catalyst that is more excellent in terms of safety and cost, and is applicable to various vinyl monomers is still desired.